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Selecting one of the following will take you directly to that section:
Enables optimizations for speed and disables some optimizations that
increase code size and affect speed.
To limit code size, this option:
- Enables global optimization; this includes data-flow analysis,
code motion, strength reduction and test replacement, split-lifetime
analysis, and instruction scheduling.
- Disables intrinsic recognition and intrinsics inlining.
The O1 option may improve performance for applications with very large
code size, many branches, and execution time not dominated by code within loops.
On IA-32 Windows platforms, -O1 sets the following:
/Qunroll0, /Oi-, /Op-, /Oy, /Gy, /Os, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Ob2, and /Og
Enables optimizations for speed. This is the generally recommended
optimization level. This option also enables:
- Inlining of intrinsics
- Intra-file interprocedural optimizations, which include:
- inlining
- constant propagation
- forward substitution
- routine attribute propagation
- variable address-taken analysis
- dead static function elimination
- removal of unreferenced variables
- The following capabilities for performance gain:
- constant propagation
- copy propagation
- dead-code elimination
- global register allocation
- global instruction scheduling and control speculation
- loop unrolling
- optimized code selection
- partial redundancy elimination
- strength reduction/induction variable simplification
- variable renaming
- exception handling optimizations
- tail recursions
- peephole optimizations
- structure assignment lowering and optimizations
- dead store elimination
On IA-32 Windows platforms, -O2 sets the following:
/Og, /Oi-, /Os, /Oy, /Ob2, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Gs, and /Gy.
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On IA-32 and Intel EM64T processors, when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets. On IA-32
Windows platforms, -O3 sets the following:
/GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2
Controls the level of memory layout transformations performed by the compiler. This option can improve cache reuse and cache locality.
This option sets the maximum number of times a loop can be unrolled, to n. For example, -unroll1 will unroll loops just once. To disable loop unrolling, use -unroll0. .
The -par-schedule option lets you specify a scheduling algorithm or a tuning method for loop iterations.
It specifies how iterations are to be divided among the threads of the team. This option affects performance
tuning and can provide better performance during auto-parallelization.
This option enables additional interprocedural optimizations for single file compilation. These optimizations are a subset of full intra-file interprocedural optimizations. One of these optimizations enables the compiler to perform inline function expansion for calls to functions defined within the current source file.
Multi-file ip optimizations that includes:
- inline function expansion
- interprocedural constant propogation
- dead code elimination
- propagation of function characteristics
- passing arguments in registers
- loop-invariant code motion
The -fast option enhances execution speed across the entire program by including the following options that can improve run-time performance:
-O3 (maximum speed and high-level optimizations)
-Qipo (enables interprocedural optimizations across files)
-QxSSSE3 (generate code specialized for Intel(R) Core(TM)2 Duo processors, Intel(R) Core(TM)2 Quad processors and Intel(R) Xeon(R) processors with SSSE3)
-Qprec-div- (disable -prec-div) where -Qprec-div improves precision of FP divides (some speed impact)
To override one of the options set by /fast, specify that option after the -fast option on the command line. The exception is the xT or QxT option which can't be overridden. The options set by /fast may change from release to release.
This option tells the compiler to generate instructions for the highest instruction set available on the compilation host processor. The instructions generated by Host differ depending on the compilation host processor.
Code is optimized for Intel(R) processors with support for AVX instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel(R) processors with support for AVX2 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel(R) processors with support for SSE 4.2 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel(R) processors with support for SSE 4.1 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel(R) processors with support for Supplemental SSE 3 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel Pentium 4 and compatible processors that supporting Streaming SIMD Extensions 2; this is the default for Intel EM64T systems. The resulting code may contain unconditional use of features that are not supported on other processors.
Code is optimized for the Intel(R) Core(TM) processor family. Code is expected to run properly on any processor that supports SSE3, SSE2 and SSE instruction sets
Code is optimized for the Intel(R) Core(TM) processor family. Code is expected to run properly on any processor that supports AVX, SSE3, SSE2 and SSE instruction sets
Code is optimized for Intel(R) Atom processors with support for Supplemental SSE 3 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Tells the auto-parallelizer to generate multithreaded code for loops that can be safely executed in parallel. To use this option, you must also specify option O2 or O3. The default numbers of threads spawned is equal to the number of processors detected in the system where the binary is compiled. Can be changed by setting the environment variable OMP_NUM_THREADS
This option enables scalar replacement performed during loop transformation. To use this option, you must also specify O3. -Qscalar-rep- disables this optimization.
Tells the compiler to assume there is no aliasing.
-Qprec-div- enables optimizations that give slightly less precise results than full IEEE division.
When you specify -Qprec-div- along with some optimizations, such as /QxT, the compiler may change floating-point division computations into multiplication by the reciprocal of the denominator. For example, A/B is computed as A * (1/B) to improve the speed of the computation.
However, sometimes the value produced by this transformation is not as accurate as full IEEE division. When it is important to have fully precise IEEE division, do not use -Qprec-div- which will enable the default -Qprec-div and the result is more accurate, with some loss of performance.
Instrument program for profiling for the first phase of two-phase profile guided otimization. This instrumentation gathers information about a program's execution paths and data values but does not gather information from hardware performance counters. The profile instrumentation also gathers data for optimizations which are unique to profile-feedback optimization.
Instructs the compiler to produce a profile-optimized
executable and merges available dynamic information (.dyn)
files into a pgopti.dpi file. If you perform multiple
executions of the instrumented program, -prof-use merges
the dynamic information files again and overwrites the
previous pgopti.dpi file.
Without any other options, the current directory is
searched for .dyn files
Enable SmartHeap and/or other library usage by forcing the linker to ignore multiple definitions if present
Enable SmartHeap library usage by forcing the linker to ignore multiple definitions
MicroQuill SmartHeap Library (32-bit) available from http://www.microquill.com/
MicroQuill SmartHeap Library (64-bit) available from http://www.microquill.com/
Enable C++ Exception Handling and RTTI
This option has the same effect as specifying /GX /GR.
This option enables C++ exception handling.
Enables C++ Run Time Type Information (RTTI).
set the stack reserve amount specified to the linker
Enable/disable(DEFAULT) use of ANSI aliasing rules in optimizations; user asserts that the program adheres to these rules.
This option enables or disables prefetch insertion optimization. The goal of prefetching is to reduce cache misses by providing hints to the processor about when data should be loaded into the cache.
Directs the compiler to inline calloc() calls as malloc()/memset()
Enables cache/bandwidth optimization for stores under conditionals (within vector loops) This option tells the compiler to perform a conditional check in a vectorized loop. This checking avoids unnecessary stores and may improve performance by conserving bandwidth.
Enable compiler to generate runtime control code for effective automatic parallelization. This option generates code to perform run-time checks for loops that have symbolic loop bounds. If the granularity of a loop is greater than the parallelization threshold, the loop will be executed in parallel. If you do not specify this option, the compiler may not parallelize loops with symbolic loop bounds if the compile-time granularity estimation of a loop can not ensure it is beneficial to parallelize the loop.
Select the method that the register allocator uses to partition each routine into regions
Multi-versioning is used for generating different versions of the loop based on run time dependence testing, alignment and checking for short/long trip counts. If this option is turned on, it will trigger more versioning at the expense of creating more overhead to check for pointer aliasing and scalar replacement.
Enables more aggressive unrolling heuristics
This option instructs the compiler to analyze and transform the program so that 64-bit pointers are shrunk to 32-bit pointers wherever it is legal and safe to do so. In order for this option to be effective the compiler must be able to optimize using the -Qipo option and must be able to analyze all library/external calls the program makes.
This option requires that the size of the program executable never exceed 2^32 bytes and all data values can be represented within 32 bits. If the program can run correctly in a 32-bit system, these requirements are implicitly satisfied. If the program violates these size restrictions, unpredictable behavior might occur.
This option places local variables, except those declared as SAVE, to the run-time stack. It is as if the variables were declared with the AUTOMATIC attribute.
It does not affect variables that have the SAVE attribute or ALLOCATABLE attribute, or variables that appear in an EQUIVALENCE statement or in a common block.
This option may provide a performance gain for your program, but if your program depends on variables having the same value as the last time the routine was invoked, your program may not function properly.
If you want to cause variables to be placed in static memory, specify /Qsave (Windows).
Disables inline expansion of all intrinsic functions.
Disables conformance to the ANSI C and IEEE 754 standards for floating-point arithmetic.
Allows use of EBP as a general-purpose register in optimizations.
This option enables most speed optimizations, but disables some that increase code size for a small speed benefit.
This option enables global optimizations.
Specifies the level of inline function expansion.
Ob0 - Disables inlining of user-defined functions. Note that statement functions are always inlined.
Ob1 - Enables inlining when an inline keyword or an inline attribute is specified. Also enables inlining according to the C++ language.
Ob2 - Enables inlining of any function at the compiler's discretion.
This option tells the compiler to separate functions into COMDATs for the linker.
This option enables read only string-pooling optimization.
This option enables read/write string-pooling optimization.
This option disables stack-checking for routines with 4096 bytes of local variables and compiler temporaries.
For mixed-language benchmarks, tell the compiler to convert routine names to lowercase for compatibility
For mixed-language benchmarks, tell the compiler to convert routine names to lowercase for compatibility
For mixed-language benchmarks, tell the compiler to assume that routine names end with an underscore
Tell the compiler to treat source files as C++ regardless of the file extension
Tell the compiler to work around incompatible treatment of commas in macros, in Visual Studio 2010.
-Qoption,string,options This option passes options to a specified tool.
string Is the name of the tool.
Here: cpp indicates the C++ preprocessor.
options Are one or more comma-separated,
valid options for the designated tool.
Here: --no_wchar_t_keyword is passed to C++ preprocessor to provide
the information that there is no wchar_t keyword.
This flag must be used with Microsoft Visual Studio 2005.
It avoids syntax errors coming from the use of wchar_t in 483.xalancbmk.
Invoke the Intel C/C++ compiler 13.1 in default mode (IA32 or Intel 64 as specified in the notes) with Visual Studio 2010 compatibility
Invoke the Intel C/C++ compiler 13.1 in default mode (IA32 or Intel 64 as specified in the notes) with Visual Studio 2008 compatibility
Invoke the Intel C/C++ compiler 13.1 in default mode (IA32 or Intel 64 as specified in the notes) with Visual Studio 2005 compatibility
Invoke the Intel Fortran compiler 13.1 in default mode (IA32 or Intel 64 as specified in the notes)
Invoke the Intel C/C++ compiler in C99 mode
Invoke the Intel C/C++ compiler 13.1 in Intel 64 mode
Compiler option to statically link in libraries at link time
Location of the Intel 64 version of the Intel Compiler libraries
Location of the Microsoft Visual Studio libraries
Location of the 64-bit versions of the Microsoft Visual Studio libraries
Location of the Microsoft Visual Studio libraries
Location of the 64-bit versions of the Microsoft Visual Studio libraries
Location of additional Microsoft Visual Studio libraries
If you set the number of threads to be equal to the number of cores, specifying KMP_AFFINITY=granularity=fine,scatter will spread the threads evenly across sockets, with one thread per physical core.